It is known that thermoplastic containers and other hollow objects can be produced by a process known as the injection blow molding process in which closed end, hollow preforms or parisons are produced by an injection molding process at a first station on a rotary molding machine. In this process each preform is injection molded around the exterior of a long, narrow member, which is usually called a core rod. The core rod, or, typically, a multiplicity of like core rods in a multiple cavity molding machine, are inserted into a face block member of a rotary turret of the molding machine, and the rotary turret with the core rods inserted into its face block is indexed, after the parisons are formed on the core rods, to a blow molding station. At the molding station, the parisons, while still at a suitable molding temperature, are blown into the configuration of containers or other hollow objects against the internal surfaces of mating mold sections. In a process of this type, each core rod is hollow, and compressed air for the blowing operation is introduced from the molding machine through the face block into each object being blown through the core rod for that object.
Because of the need to maintain a positive pressure within a container or other object while it is being blown to accomplish the blowing operation, it is necessary to provide a suitable seal between each core rod and an opening in the molding machine face block which receives an end of such core rod. Heretofore, it was customary to effect such seal by inserting an elastomeric O-ring in an annular groove in the inside surface of each core rod receiving opening of the face block. Such an O-ring would then seal against an outside diametral surface of the core rod, and would serve to prevent blowing air leakage from the molding machine through an annular opening between the inside of the face block opening and the outside of the core rod. However, the use of such a seal limits radial movement of the core rod relative to the face block that is, movement transverse to the longitudinal central axis of the core rod, and such radial movement may be desirable to accommodate possible misalignment between the core rod and other elements of the mold tooling during the blowing operation. With the diametral seal against the core rod, as described above, misalignment of the core rod and the mold tooling is accommodated mainly by angular deflection of the core rod about an axis extending through the face block O-ring, that is, about an axis extending transversely of the longitudinal central axis of the core rod. Such angular deflection can be disadvantageous in a container forming operation, however, especially if more than a small degree thereof occurs, because it can lead to excessive and premature wear of the core rods and the bottle finish forming neck rings of the mold tooling, which are moved into close proximity to the core rod during a container blowing operation. Further, in certain situations such core rod angular deflection can lead to undesirable variations in the thickness of the sidewall of a container which is being produced by such tooling.